1. Field of the Invention
The present invention generally relates to a method for manufacturing a semiconductor device and, more particularly, to a method for grinding and dicing a large-diameter wafer to produce a semiconductor device having a reduced thickness.
In a manufacturing process of a semiconductor device, a wafer on which circuit patterns are formed is subjected to a grinding process so as to reduce a thickness of the wafer. The grinding is applied to a surface (back surface) on which no circuit pattern is formed.
In recent years, large-diameter wafers have been used to improve productivity of semiconductor devices. Additionally, since semiconductor devices having a small thickness have been required for use in an IC card, it is required to reduce a thickness of a wafer. Further, use of a wafer having bumps, which bumps are formed before the wafer is subjected to dicing, has been increased. However, an increase in a diameter of the wafer, reduction in a thickness of the wafer and the wafer having bumps may increase a possibility of wafer cracking during a manufacturing process.
For example, when a large-diameter wafer is ground, a thickness of the wafer is limited to about 200 .mu.m. That is, if the wafer is ground to a thickness of less than 200 .mu.m, the wafer may frequently crack during the grinding process and a handling process.
Additionally, in the wafer having bumps, a possibility of wafer cracking during the grinding process is increased since the bumps act as protrusions.
Accordingly, it is desired to establish a technique for grinding and dicing a large-diameter wafer at a high throughput without damaging the wafer.
2. Description of the Related Art
A description will now be given, with reference to FIGS. 1 to 6, of a conventional manufacturing method of a semiconductor device. The manufacturing method of a semiconductor device includes a grinding process and a dicing process. In the grinding process, grinding (referred to as back grinding) is applied to a back surface of a wafer so that a thickness of the wafer is reduced to a predetermined thickness. In the dicing process, dicing is applied to the wafer so that the wafer is divided into a plurality of individual semiconductor chips.
FIG. 1 is a flowchart of a conventional manufacturing method of a semiconductor device in which method a dicing process and a grinding process are performed. The conventional method shown in FIG. 1 comprises the steps of: applying a protective tape to a wafer having a front surface on which circuits are formed (step S10); grinding a back surface of the wafer (step S20); applying a dicing tape to the wafer after turning over the wafer (step S14); and dicing the wafer from the side of the front surface (step S16).
FIG. 2 is an illustration for explaining the protective tape applying process (step S10) shown in FIG. 1. FIG. 3 is an illustration for explaining the grinding process (step S12) shown in FIG. 1. FIG. 4 is an illustration for explaining the dicing tape applying process (step S14) shown in FIG. 1. FIG. 5 is an illustration for explaining the dicing process (step S16) shown in FIG. 1.
Semiconductor circuits are previously formed on a front surface of a wafer 10 to be ground. First, as shown in FIG. 2, a protective tape 12 is applied to the front surface of the wafer 10 so as to protect the semiconductor circuits formed on the front surface of the wafer 10. Then, the wafer 10 is fixed by suction on a vacuum chuck table via the protective tape 12. The protective tape 12 is formed of a resin, and an ultraviolet cure pressure-sensitive adhesive is applied to a surface thereof. The wafer 10 is ground in a state in which the wafer 10 is fixed on the vacuum chuck table via the protective tape 12.
In the grinding process, the back surface of the wafer 10 is ground by using a grinding tool 18 as shown in FIG. 3 so as to reduce a thickness of the wafer 10 to a predetermined thickness. Specifically, the grinding is performed by moving the rotating grinding tool 18 in directions indicated by arrows X1 and X2 while supplying a grinding liquid. Thereby, the wafer 10 having the predetermined thickness is formed.
After the grinding process is completed, the wafer 10 is removed from the protective tape 12. Then, the wafer 10 is applied to a dicing tape 20 which is spread on a wafer frame 14 so that the front surface of the wafer 10 on which front surface the circuits are formed faces upwardly as shown in FIG. 4. The dicing tape 20 is formed of a resin, and the pressure-sensitive adhesive is applied to a surface of the dicing tape 20. The wafer 10 is diced in a state in which the wafer 10 is secured on the dicing tape 20 by the pressure-sensitive adhesive.
In the dicing process, the wafer 10 is diced by using a dicing saw 22 as shown in FIG. 5. The dicing is performed while monitoring an image of a scribe line formed on the front surface of the wafer 10. Thereby, the wafer 10 is divided into a plurality of semiconductor chips 11.
According to the above-mentioned conventional method, a pressing force is applied to a part of the wafer 10 by the grinding tool 18 since the grinding process is performed prior to the dicing process. When the thickness of the wafer 10 is reduced to less than 200 .mu.m by grinding, the strength of the wafer 10 is reduced. Accordingly, the wafer may crack during the grinding process. Particularly, when the thickness of the wafer 10 is reduced to 50 .mu.m by grinding, there is a problem in that wafer cracks may frequently occur. Additionally, when the wafer 10 is provided with bumps, the bumps may act as protrusions and the grinding is performed in a state in which the wafer 10 is placed on the protrusions. Thus, a possibility of occurrence of cracking in the wafer 10 is further increased.
Additionally, in the above-mentioned conventional method, after the wafer 10 is ground to the predetermined thickness, the protective tape 12 is removed and the wafer 10 is turned over. That is, the back surface of the wafer 10 faces upwardly when the grinding process is completed. Accordingly, in order to perform the dicing from the side of the front surface, the wafer 10 is applied on the dicing tape 20 with the front surface of the wafer 10 facing upwardly.
However, since the thickness of the wafer 10 is reduced by grinding, the wafer 10 warps as shown in FIG. 6 after the protective tape 12 is removed. A degree of warpage of the wafer 10 can be represented by a maximum distance (indicated by an arrow H in FIG. 6) between the dicing tape 20 and the wafer 10. If a 6-inch wafer is ground to a thickness of 200 .mu.m, a warpage of about 2 cm (H=2 cm) is generated. Additionally, if an 8-inch wafer is ground to a thickness of 200 .mu.m, a warpage of about 3 cm (H=3 cm) is generated.
If a warpage is generated in the wafer 10 as mentioned above, there is a problem in that the wafer 10 cannot be properly handled. In a worst case, the wafer may crack during the handling.